The temperature-field information collected by infrared CCD is usually interfered by various measurement errors, including optical system error, CCD error and infrared radiation interference. Errors induced by optical system and CCD can usually be controlled by image processing techniques. However, these techniques can hardly deal with infrared radiation interferences due to their high randomness. To solve this problem, a series of thermo-couples were preset to monitor temperatures at fixed points, which were used to calibrate the system emissivity. Real-time measurement of temperature field was thus achieved based on the modified system emissivity. The mathematical model and system of calibration are established to prevent the sudden change of temperature with system emissivity. Error and mutation of the on-line temperature field measurement are eliminated. The test results show the feasibility of the calibration system of on-line temperature-field measurement.